The present invention relates to a buffer device for data on a bus or a data buffer device, and more particularly to a data buffer device in which data is inputted and outputted with a plurality of words as a minimum unit, and a data buffer array device in which such devices are arrayed one-dimensionally or two-dimensionally.
In the related art, when a device on a bus is to be accessed, a device designation signal (which is usually an address signal or device selection signal) must assure,. predetermined set-up time and hold time relative to a read strobe signal or write strobe signal. Thus, if the device to be accessed is shifted from a device designation A to a device designation B, it is necessary to change the address to B after the access at the address A has been completed, and start the access to B after the signal has been sufficiently stabilized. As a result, when the access is to be shifted between devices, a longer time than a sum of the set-up time and the hold time is spent, and continuous transfer of data cannot be attained and usage efficiency of the bus is low.
Where the access to the device B is permitted depending on a status of the device B, it is necessary to check the status of the device B prior to the access to the device B. This further lowers the usage efficiency of the bus. In order to solve the above problem, it has been proposed to improve the usage efficiency of the bus by pipelining the protocol of the bus. Namely, the bus may be used without waste by preassigning a time in which the bus may be used for the data transfer by staggering the times for three stages, that is, send-out of the device designation signal, acknowledgement of availability of the designated device and transfer of data.
However, in this method, each device must have a relatively complex bus control unit and a waste time corresponding to several pipeline stages takes place if the designated device is not available.
In the prior art method, when the access is to be shifted from one device to another device, a certain time interval must always be spent. This lowers the usage efficiency of the bus. While the pipeline method has been known as a means for preventing the reduction of the usage efficiency of the bus, the bus control therefor is complex and the usage efficiency of the bus is significantly lowered when the pipeline is frequently disturbed.